Swift

What is a State Pattern? The State Pattern allows an object to alter its behavior when its internal state changes. The object will appear to change its class. Source What problems does it solve? Complex conditional logic: When an object’s behavior depends on its internal state, it often leads to complex conditional statements. The State pattern simplifies this by encapsulating each state and its behavior in separate classes, making the code more readable and maintainable. State-specific behavior: Objects often need to change their behavior based on their state. The State pattern allows objects to delegate behavior to state objects, which can vary independently. This promotes better encapsulation and separation of concerns. Adding new states: When new states need to be added, the State pattern makes it easier to extend the functionality without modifying existing code. New states can be added by creating new state classes and integrating them into the existing context, without changing the context class itself. Real-world code example // Define the VendingMachine protocol protocol VendingMachineState { func insertCoin() func dispenseItem() } // Define concrete states class NoCoinState: VendingMachineState { private let vendingMachine: VendingMachine init(vendingMachine: VendingMachine) { self.vendingMachine = vendingMachine } func insertCoin() { print("Coin inserted") // Transition to the HasCoinState vendingMachine.changeState(newState: vendingMachine.hasCoinState) } func dispenseItem() { print("Please insert a coin first") } } class HasCoinState: VendingMachineState { private let vendingMachine: VendingMachine init(vendingMachine: VendingMachine) { self.vendingMachine = vendingMachine } func insertCoin() { print("Coin already inserted") } func dispenseItem() { if vendingMachine.inventoryCount > 0 { print("Item dispensed") vendingMachine.decreaseInventory() // Transition to the NoCoinState vendingMachine.changeState(newState: vendingMachine.noCoinState) } else { print("Out of stock") } } } // Define the VendingMachine class class VendingMachine { var inventoryCount: Int = 5 var currentState: VendingMachineState! var noCoinState: VendingMachineState! var hasCoinState: VendingMachineState! init() { noCoinState = NoCoinState(vendingMachine: self) hasCoinState = HasCoinState(vendingMachine: self) currentState = noCoinState } func changeState(newState: VendingMachineState) { currentState = newState } func insertCoin() { currentState.insertCoin() } func dispenseItem() { currentState.dispenseItem() } func decreaseInventory() { inventoryCount -= 1 } } // Usage let vendingMachine = VendingMachine() vendingMachine.dispenseItem() vendingMachine.insertCoin() vendingMachine.insertCoin() vendingMachine.dispenseItem() vendingMachine.dispenseItem() Thank you for reading! ...

What is a Dependency Inversion Principle? The Dependency Inversion Principle means that high-level modules should not depend on low-level modules. Source Source What problems does it solve? The Dependency Inversion Principle (DIP) helps solve: Rigidity Fragility Immobility problems Real-world code example Violation of DIP // High-level module directly depending on low-level modules class MessageService { func sendMessageViaEmail(message: String) { let emailSender = EmailSender() emailSender.sendMessage(message: message) } func sendMessageViaSMS(message: String) { let smsSender = SMSSender() smsSender.sendMessage(message: message) } func sendMessageViaPushNotification(message: String) { let pushNotificationSender = PushNotificationSender() pushNotificationSender.sendMessage(message: message) } } Adhering to DIP // Protocol defining the interface for sending messages protocol MessageSender { func sendMessage(message: String) } // High-level module depending on abstraction (MessageSender protocol) class MessageService { private let messageSender: MessageSender init(messageSender: MessageSender) { self.messageSender = messageSender } func sendMessage(message: String) { messageSender.sendMessage(message: message) } } // Concrete implementations of MessageSender protocol for different channels class EmailSender: MessageSender { func sendMessage(message: String) { print("Sending email: \(message)") } } class SMSSender: MessageSender { func sendMessage(message: String) { print("Sending SMS: \(message)") } } class PushNotificationSender: MessageSender { func sendMessage(message: String) { print("Sending push notification: \(message)") } } // Example usage let emailSender = EmailSender() let smsSender = SMSSender() let pushNotificationSender = PushNotificationSender() let emailService = MessageService(messageSender: emailSender) let smsService = MessageService(messageSender: smsSender) let pushNotificationService = MessageService(messageSender: pushNotificationSender) emailService.sendMessage(message: "Hello via email") smsService.sendMessage(message: "Hello via SMS") pushNotificationService.sendMessage(message: "Hello via push notification") Thank you for reading! 😊

When was it introduced? It was introduced in Swift 5.5 at WWDC 2021. You can find the more comprehensive info about Modern Concurrency in Swift Concurrency Manifesto. What are actors? Actors eliminate shared mutable state and explicit synchronization through deep copying of all the data that passed to an actor to a message sent and preventing direct access to actor state. Actors are reference types. actor DatabaseManager { private var data: [String: String] = [:] func readData(key: String) -> String? { data[key] } func writeData(key: String, value: String) { data[key] = value } } What is an asynchronous function? The asynchronous function or asynchronous method can be suspended while it is partway through execution. It can pause in the middle when it’s waiting for something. ...

What is the Thread? A Thread is a small set of instructions that can be executed independently from the main program. Threads are often used to improve program performance by allowing multiple tasks to be executed at the same time. The Thread has its own stack, registers, and program counters. Threads share memory address space, and it is possible to communicate between Threads using shared memory space. ...

What is DispatchGroup? DispatchGroup provides a mechanism to track the completion group of tasks. How DispatchGroup works? DispatchGroup has three main methods, enter, leave and notify, that allow you to control the completion of a specific task. let dispatchGroup = DispatchGroup() dispatchGroup.enter() dispatchGroup.leave() dispatchGroup.notify(queue: .main) {} Let`s talk about each of these methods. enter — manually indicate a block has entered group. leave — manually indicate a block in the group has been completed. notify(queue: ) — schedule a block to be submitted to a queue when all the blocks associated with a group have been completed. The queue parameter is the queue to which the supplied block will be submitted when the group is complete. ...